Dipole loudspeaker for producing sound at bass frequencies

Abstract

A dipole loudspeaker for producing sound at bass frequencies. The dipole loudspeaker includes: a diaphragm having a first radiating surface and a second radiating surface, wherein the first radiating surface and the second radiating surface are located on opposite faces of the diaphragm; a drive unit configured to move the diaphragm at bass frequencies such that the first and second radiating surfaces produce sound at bass frequencies, wherein the sound produced by the first radiating surface is in antiphase with sound produced by the second radiating surface; a frame, wherein the diaphragm is suspended from the frame via one or more suspension elements, wherein the frame is configured to allow sound produced by the first radiating surface to propagate out from a first side of the dipole loudspeaker and to allow sound produced by the second radiating surface to propagate out from a second side of the dipole loudspeaker. The diaphragm includes a region of porous material having a specific airflow resistance in the range 5-5000 Pa·s/m, wherein the diaphragm is configured to permit airflow through at least part of said region of porous material from the first radiating surface of the diaphragm to the second radiating surface of the diaphragm.

What is claimed is: 
     
       1. A dipole loudspeaker for producing sound at bass frequencies, the dipole loudspeaker including:
 a diaphragm having a first radiating surface and a second radiating surface, wherein the first radiating surface and the second radiating surface are located on opposite faces of the diaphragm; 
 a drive unit configured to move the diaphragm at bass frequencies such that the first and second radiating surfaces produce sound at bass frequencies, wherein the sound produced by the first radiating surface is in antiphase with sound produced by the second radiating surface; 
 a frame, wherein the diaphragm is suspended from the frame via one or more suspension elements, wherein the frame is configured to allow sound produced by the first radiating surface to propagate out from a first side of the dipole loudspeaker and to allow sound produced by the second radiating surface to propagate out from a second side of the dipole loudspeaker; 
 wherein the diaphragm includes a region of porous material having a specific airflow resistance in the range 50-500 Pa·s/m, wherein the diaphragm is configured to permit airflow through at least part of said region of porous material from the first radiating surface of the diaphragm to the second radiating surface of the diaphragm. 
 
     
     
       2. A dipole loudspeaker according to  claim 1 , wherein the dipole loudspeaker is configured for use with an ear of a user located at a listening position that is in front of and 30 cm or less from the first radiating surface of the diaphragm. 
     
     
       3. A dipole loudspeaker according to  claim 1 , wherein the diaphragm includes a layer of porous material mounted on a supporting structure. 
     
     
       4. A dipole loudspeaker according to  claim 3 , wherein the supporting structure is a rigid perforated sheet of non-porous material, wherein the sheet includes a plurality of holes/cut-outs. 
     
     
       5. A dipole loudspeaker according to  claim 4 , wherein the plurality of holes/cut-outs having an area that is 50% or more of the area of the sheet when the holes/perforations are covered. 
     
     
       6. A dipole loudspeaker according to  claim 3 , wherein a lead wire configured to supply electrical energy to a voice coil of the drive unit is mounted to the supporting structure. 
     
     
       7. A dipole loudspeaker according to  claim 1 , wherein the diaphragm is an unsupported layer of porous material. 
     
     
       8. A dipole loudspeaker according to  claim 1 , wherein the dipole loudspeaker includes a supplementary loudspeaker configured to produce sound which propagates through the at least part of said region of porous material. 
     
     
       9. A dipole loudspeaker according to  claim 8 , wherein the supplementary loudspeaker is a mid-high frequency loudspeaker configured to produce sound across at least the range 500 Hz-10 kHz. 
     
     
       10. A dipole loudspeaker according to  claim 1 , wherein the drive unit is rigidly attached to the frame of the dipole loudspeaker. 
     
     
       11. A seat assembly including a seat and a dipole loudspeaker for producing sound at bass frequencies, the dipole loudspeaker including:
 a diaphragm having a first radiating surface and a second radiating surface, wherein the first radiating surface and the second radiating surface are located on opposite faces of the diaphragm; 
 a drive unit configured to move the diaphragm at bass frequencies such that the first and second radiating surfaces produce sound at bass frequencies, wherein the sound produced by the first radiating surface is in antiphase with sound produced by the second radiating surface; 
 a frame, wherein the diaphragm is suspended from the frame via one or more suspension elements, wherein the frame is configured to allow sound produced by the first radiating surface to propagate out from a first side of the dipole loudspeaker and to allow sound produced by the second radiating surface to propagate out from a second side of the dipole loudspeaker; 
 wherein the diaphragm includes a region of porous material having a specific airflow resistance in the range 50-500 Pa·s/m, wherein the diaphragm is configured to permit airflow through at least part of said region of porous material from the first radiating surface of the diaphragm to the second radiating surface of the diaphragm; 
 wherein the seat is configured to position a user who is sat down in the seat such that an ear of the user is located at a listening position that is in front of and 30 cm or less from the first radiating surface of the diaphragm. 
 
     
     
       12. A seat assembly including  claim 11 , wherein the dipole loudspeaker is mounted within a headrest of the seat. 
     
     
       13. A seat assembly according to  claim 12 , wherein the headrest includes a headrest material which at least partially encloses the dipole loudspeaker, wherein the headrest material which encloses the dipole loudspeaker is a porous material having a specific airflow resistance of less than 25 Pa·s/m. 
     
     
       14. A seat assembly according to  claim 11 , wherein the headrest includes two of the dipole loudspeakers, wherein the seat is configured to position a user who is sat down in the seat such that a first ear of the user is located at a listening position that is in front of and 30 cm or less from the first radiating surface of the diaphragm of a first of the two dipole loudspeakers, and such that a second ear of the user is located at a listening position that is in front of and 30 cm or less from the first radiating surface of the diaphragm of a second of the two dipole loudspeakers.